After receiving his Juris Doctor degree from UC Hastings College of the Law in 1980, he was appointed an Assistant U.S. Attorney in Orange County. He had a 100% conviction rate prosecuting drug dealers, gang members, white collar criminals, and civil rights cases. In addition, he also served as a military prosecutor during between 1980 and 1985.

In 2000, Umberg left the Clinton administration and returned to California. In 2002, he lost the Democratic Party nomination for State Insurance Commissioner to John Garamendi. In 2004, Umberg won election to the Assembly to represent the 69th District. During his third term, Umberg Chaired the Elections and Redistriciting Committee. While in the legislature, Umberg authored over 60 measures which became law. These laws include measures dealing with hate crimes, white collor crime, campaign finance reform, high-speed rail transport and school meal programs.

Umberg sought the seat of retiring State SenatorJoe Dunn (D) in the 2006 elections. Orange County Supervisor and former Assemblyman Lou Correa jumped in the race in January 2006 despite pressure from the local Democratic party for him to stay out (although with pressure from the state Democratic party for him to jump in), stating that he was running in part because of the allegations about Umberg's residency. Aside from other negative articles,[1] Umberg also received criticism that he voted to legalize gay marriage.[2] Umberg attempted to get Correa off the ballot because Correa submitted more than the number of signatures required to qualify for the ballot, but ultimately failed.[3] Umberg also claimed that an alliance between Correa and State Senate President Pro Tem Don Perata to funnel funds to Correa's campaign was illegal.[4] Umberg was defeated by Correa by a 60% to 40% margin, and Correa went on to narrowly win the general election.

After Correa won the general election for the Senate by a 10% margin, Umberg entered the race to replace Correa on the Orange County Board of Supervisors, representing the 1st Supervisorial District. 52% of 1st Supervisorial District voters are also voters in the 69th Assembly District, formerly represented by Umberg. 73% of 1st Supervisorial District voters are also 34th Senate District voters, so Umbert was believed to be the favorite. On 6 February 2007, Umberg received 21.4%, coming in third, less than he had been expected to poll.[5]

On June 23, 2005, Umberg admitted to the Los Angeles Times that he had an extramarital affair. Umberg stated that the woman was attempting to confront the Umbergs at his home, at school events, and in the gallery of the Assembly, and had forwarded e-mail messages exchanged during the affair to the Orange County Register. Separately, on June 24, 2005, the Register reported that, contrary to claims made by his 2004 Assembly campaign, Umberg only spent 16 days in Guantanamo Bay for his 2004 tour of duty. On July 15, 2005, the Register retracted some of its claims about Umberg.[6]